Abstract
Naphthalene, a selective pulmonary bronchiolar cytotoxicant in the mouse, is metabolized in the liver to reactive metabolites that are capable of circulating and becoming bound irreversibly in extrahepatic tissues in vivo. Circulating reactive metabolites generated in the liver could interact with extrahepatic tissues either directly to produce toxicity or indirectly by depleting cellular defense capabilities. The studies reported here were to determine whether naphthalene oxide, an obligate and unstable intermediate in the metabolism of naphthalene, is capable of diffusing from intact hepatocytes. Efflux was measured by trapping the epoxide with [3H]glutathione followed by subsequent quantitation of the labeled glutathione adducts. Seventeen to 35% of the total amount of naphthalene oxide formed intracellularly was trapped extracellularly in 15- and 30-min incubations. The quantity of naphthalene oxide effluxing from isolated hepatocytes increased with increasing substrate concentrations. However, the relative amount of epoxide leaving the cell as a percentage of the total formed did not change over naphthalene concentrations ranging from 0.015 to 1.5 mM. Reactive naphthalene metabolites capable of binding covalently to extracellular proteins diffused from isolated hepatocytes in a time- and concentration-dependent manner. The ratio of extracellular to intracellular covalent binding was dependent upon the concentration of naphthalene in the incubation; at low naphthalene concentrations, covalent binding was higher extracellularly than intracellularly, whereas, at high concentrations, metabolites were predominantly bound intracellularly. These studies suggest that there is no threshold for the efflux of naphthalene oxide but that the relative amounts of reactive metabolite bound intra- vs. extracellularly may depend upon saturation of intracellular detoxication capabilities.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 485-492 |
| Number of pages | 8 |
| Journal | Journal of Pharmacology and Experimental Therapeutics |
| Volume | 242 |
| Issue number | 2 |
| State | Published - 1987 |
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ASJC Scopus subject areas
- Pharmacology
Cite this
Efflux of naphthalene oxide and reactive naphthalene metabolites from isolated hepatocytes. / Richieri, P. R.; Buckpitt, Alan R.
In: Journal of Pharmacology and Experimental Therapeutics, Vol. 242, No. 2, 1987, p. 485-492.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Efflux of naphthalene oxide and reactive naphthalene metabolites from isolated hepatocytes
AU - Richieri, P. R.
AU - Buckpitt, Alan R
PY - 1987
Y1 - 1987
N2 - Naphthalene, a selective pulmonary bronchiolar cytotoxicant in the mouse, is metabolized in the liver to reactive metabolites that are capable of circulating and becoming bound irreversibly in extrahepatic tissues in vivo. Circulating reactive metabolites generated in the liver could interact with extrahepatic tissues either directly to produce toxicity or indirectly by depleting cellular defense capabilities. The studies reported here were to determine whether naphthalene oxide, an obligate and unstable intermediate in the metabolism of naphthalene, is capable of diffusing from intact hepatocytes. Efflux was measured by trapping the epoxide with [3H]glutathione followed by subsequent quantitation of the labeled glutathione adducts. Seventeen to 35% of the total amount of naphthalene oxide formed intracellularly was trapped extracellularly in 15- and 30-min incubations. The quantity of naphthalene oxide effluxing from isolated hepatocytes increased with increasing substrate concentrations. However, the relative amount of epoxide leaving the cell as a percentage of the total formed did not change over naphthalene concentrations ranging from 0.015 to 1.5 mM. Reactive naphthalene metabolites capable of binding covalently to extracellular proteins diffused from isolated hepatocytes in a time- and concentration-dependent manner. The ratio of extracellular to intracellular covalent binding was dependent upon the concentration of naphthalene in the incubation; at low naphthalene concentrations, covalent binding was higher extracellularly than intracellularly, whereas, at high concentrations, metabolites were predominantly bound intracellularly. These studies suggest that there is no threshold for the efflux of naphthalene oxide but that the relative amounts of reactive metabolite bound intra- vs. extracellularly may depend upon saturation of intracellular detoxication capabilities.
AB - Naphthalene, a selective pulmonary bronchiolar cytotoxicant in the mouse, is metabolized in the liver to reactive metabolites that are capable of circulating and becoming bound irreversibly in extrahepatic tissues in vivo. Circulating reactive metabolites generated in the liver could interact with extrahepatic tissues either directly to produce toxicity or indirectly by depleting cellular defense capabilities. The studies reported here were to determine whether naphthalene oxide, an obligate and unstable intermediate in the metabolism of naphthalene, is capable of diffusing from intact hepatocytes. Efflux was measured by trapping the epoxide with [3H]glutathione followed by subsequent quantitation of the labeled glutathione adducts. Seventeen to 35% of the total amount of naphthalene oxide formed intracellularly was trapped extracellularly in 15- and 30-min incubations. The quantity of naphthalene oxide effluxing from isolated hepatocytes increased with increasing substrate concentrations. However, the relative amount of epoxide leaving the cell as a percentage of the total formed did not change over naphthalene concentrations ranging from 0.015 to 1.5 mM. Reactive naphthalene metabolites capable of binding covalently to extracellular proteins diffused from isolated hepatocytes in a time- and concentration-dependent manner. The ratio of extracellular to intracellular covalent binding was dependent upon the concentration of naphthalene in the incubation; at low naphthalene concentrations, covalent binding was higher extracellularly than intracellularly, whereas, at high concentrations, metabolites were predominantly bound intracellularly. These studies suggest that there is no threshold for the efflux of naphthalene oxide but that the relative amounts of reactive metabolite bound intra- vs. extracellularly may depend upon saturation of intracellular detoxication capabilities.
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M3 - Article
VL - 242
SP - 485
EP - 492
JO - Journal of Pharmacology and Experimental Therapeutics
JF - Journal of Pharmacology and Experimental Therapeutics
SN - 0022-3565
IS - 2
ER -